Generally, for producing a desired semiconductor device, a heat treatment such as a film forming processing or a pattern etching processing or the like is repeatedly performed on a semiconductor wafer. With a recent trend towards high-density and high-integration of a semiconductor device, a strict heat treatment method has been demanded. For example, for a very thin oxide film such as an insulating film of a capacitor or a gate insulating film in the device, the film is also required to be more thin, and at the same time, to have more superior insulation property.
As for such an insulating film, a silicon oxide film, a silicon nitride film or the like has been used. Recently, a metal oxide film, e.g., a tantalum oxide (Ta2O5) or the like, is preferably used as a material having further improved excellent insulation characteristic (e.g., Japanese Patent Laid-open Application No. H2˜283022). The metal oxide film shows reliable high insulation property even though it is thin as an oxide film conversion film.
For forming a metal oxide film having good characteristics, temperature of the semiconductor wafer needs to be very accurately controlled during the film formation. For example, a case of forming a tantalum oxide will be explained. First, a semiconductor wafer is loaded into a film forming device. As disclosed in the aforementioned application, a metal alkoxide (Ta(O2H5)5) of tantalum is used as a source for film formation. The metal alkoxide (Ta(O2H5)5) is supplied into the film forming device while being bubbled by nitrogen gas or the like. Meanwhile, the semiconductor wafer is maintained at a process temperature of, e.g., about 450° C. Further, a tantalum oxide (Ta2O5) film is deposited on the semiconductor wafer by CVD (Chemical Vapor Deposition) under a vacuum atmosphere.
As for another kind of film, an oxide film containing a plurality of metal components, i.e., so-called a multi-component metal oxide thin film, is used as a nonvolatile memory since it has ferroelectricity. As a typical example of the multi-component metal oxide thin film, a PZT film (oxide film of Pb, Zr and Ti) has been known.
In case when forming a metal oxide film, a complex metallic material film or the like, it is preferable to conduct a temperature management on the wafer. In a conventional device, a thermocouple as a temperature detection unit is provided in a mounting table (susceptor) for mounting thereon a wafer, and the temperature of the wafer is indirectly detected. Based on this detection value, an output of a heating unit such as a heating lamp, a heater or the like is controlled to thereby control the temperature of the wafer.
However, what the aforementioned thermocouple directly detects is the temperature of the mounting table, not that of the wafer as described above. Thus, a real temperature of the wafer can somewhat differ from the detection value.
For the same reason, e.g., Japanese Patent Laid-open Application No. H8˜264472, Japanese Patent Laid-open Application No. H11˜45859, Japanese Patent Laid-open Application No. H5˜152208 and the like disclose that the temperature of the wafer is measured by using a radiation thermometer without using the thermocouple. The radiation thermometer detects temperature of an object by measuring radiation brightness in a specific wavelength band from the object. By using the radiation thermometer, it is possible to directly measure the temperature of the wafer accurately without making any direct contact with the object.
However, if a residual thin film is deposited to be adsorbed on a surface of a light detector of the radiant thermometer on which an incident light of specific wavelength band from the wafer is to be illuminated, the light is absorbed by the thin film, and therefore, the radiant thermometer cannot measure the temperature of the wafer accurately. Thus, for the purpose of preventing an unnecessary thin film from being deposited on the surface of the light detector, which is exposed to a processing space while a film forming processing is performed on the wafer (or on a surface of a transparent glass plate or the like, for partitioning the incident surface from the processing space), it is preferable to supply a nonreactive gas into an observation hole, to which the radiant thermometer is attached, thereby purging a film forming gas.
However, if the nonreactive gas for preventing the deposition of the thin film is introduced into the processing space, a partial pressure of a source gas needed for forming, e.g., a metal oxide film (e.g., a source gas for pentoethoxytantalum or PZT) is lowered. As a result, a film thickness of a portion, into which the nonreactive gas is introduced, is changed, so that uniformity in the film thickness of in-surface of the wafer becomes deteriorated. Further, an increase in the amount of nonreactive gas to be used is problematic.